What a person does, even while intoxicated. IS their responsibility.

"I was drunk" is not an adequate reason to absolve people of personal responsibility. If someone signs a contract or enters a verbal agreement while drunk it is still legally applicable in most states. This being the case. I don't see consent as a special circumstance. It is not the states job to save people from themselves.

Prove she was legally intoxicated

Unless you can prove she was legally intoxicated at the time, how can you prove she was unable to give consent? Look at it the other way around. If a man reported that he was raped the night before by a woman because he claimed that even though he consented at the time, he was unable to because he was drunk, he would be laughed out of the room.

She gave consent

I personally believe that you cannot prove beyond a reasonable doubt that the girl would have declined the offer while sober and regret does not equal rape. I also question what would happen if the tables were turned and a sober girl had sex with a male who was drunk would she be called a predator and convicted of rape?